Deconvolution of Smectite Hydration Isotherms

Sorption isotherm models have traditionally served as an invaluable tool to characterize synthesized and natural mineral particles. However, for particles susceptible to substantial hydration, such as the swelling smectite clay minerals and other layered minerals displaying intercalation of discrete water monolayers, traditional isotherm models inadequately describe the total water uptake as a result of the change in available surface sites and area during the hydration process. With the goal of deconvoluting the water uptake behavior of swelling smectite minerals, this research presents a novel composite isotherm model that describes water uptake by surface adsorption, condensation, and stepwise intercalation. A set of eight montmorillonite samples ion-exchanged with different countercations (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, and Cu2+) were used to develop this model, which was based on gravimetric uptake measurements and X-ray diffraction data of basal spacings obtained from relative humidity conditions up to 98% relative humidity.